Send notifications when user is no longer out-of-office

Fixes bug#9257.
OutOfOffice is true when the checkbox in the user prefs has been turned on by
the agent.
However, if the out-of-office period is in the past, the checkbox can still
be enabled but the user should receive notifications. This is achieved by
checking OutOfOfficeMessage which is provided by GetUser(), and that takes
the dates into account.